1. Field of the Invention
The present invention relates to a motor-operated valve apparatus driving a flow control valve such as a thermal power control valve of a gas cooking appliance by a stepping motor.
2. Description of the Related Art
In a motor-operated valve apparatus operating a flow control valve using a stepping motor as an actuator, the amount of displacement of the flow control valve matches the number of pulses supplied to the stepping motor (hereinafter referred to simply as motor in this section). That is, the amount of rotation of the motor per pulse is fixed and accordingly, the amount of displacement (amount of change in opening degree) of the flow control valve per pulse is fixed. In this motor-operated valve apparatus, the number of pulses supplied to the motor defines a relative amount of change in opening degree of the flow control valve, and therefore for controlling the opening degree (displacement position) of the flow control valve to be a desired opening degree, it is necessary to determine the position of the flow control valve when apparatuses including means for controlling the motor-operated valve apparatus (microcomputer, etc.) and a motor drive circuit are powered up or initialized just thereafter.
As a method for determining the position of the flow control valve, a method in which the flow control valve is forcefully displaced to the end position of a motion range of the flow control valve (fully closed position, fully opened position or the like of the flow control valve which is hereinafter referred to as home position) mechanically restrained (by contact or fitting between members) by a stopper, a valve seat and the like (so called a shift to the home position is made) is known.
In this case, a method in which regardless of the opening degree of the flow control valve during power-up, a predetermined number of pulses sufficient to displace the flow control valve to the home position are supplied to the motor to forcefully the flow control valve to the home position has been previously known (see, for example, paragraph [0006] of Japanese Patent Laid-Open No. 6-213348 (patent document 1)).
However, this method has a problem such that if the initial position of the flow control valve is close to the home position, the motor is driven with an excessive number of pulses even after the flow control valve arrives at the home position and is forcefully stopped at the position, and therefore a disorder of the motor, abnormal sounds and vibrations occur for a relatively long time period. Because the disorder of the motor occurs for a long time period, the lifetime of the motor tends to decrease.
Thus, techniques for solving the problem are disclosed in the patent document 1 and Japanese Patent Laid-Open No. 2003-329698 (patent document 2). A similar motor control technique is disclosed in, for example, Japanese Patent No. 2502515 (patent document 3).
In the techniques found in the patent documents 1 to 3, means for detecting arrival of the flow control valve or a rotor of the motor at the home position is provided, and the supply of pulses to the motor is stopped according to the detection by the means.
In the techniques proposed in the patent documents 1 to 3, pulsed drive of the motor can be stopped when the flow control valve or the rotor of the motor arrives at the home position, thus making it possible to prevent occurrence of the disorder of the motor, abnormal sounds and vibrations. Hence, the techniques have a problem such that since detection means for detecting arrival of the flow control valve or the rotor of the motor at the home position is required, costs are disadvantageously increased, and product structures are complicated. In particular, if a thermal power control valve and a motor for driving the valve are provided for each burner as in a gas cooking appliance having a plurality of burners, the above problem is more significant.
The present invention has been made in view of such a background, and its object is to provide a motor-operated valve apparatus which can shift the flow control valve to the home position while preventing occurrence of the disorder of the stepping motor, abnormal sounds and vibrations in a simple configuration without requiring means for detecting arrival of the flow control valve at the home position.